CN113889671A

CN113889671A - Electrolyte and lithium ion battery

Info

Publication number: CN113889671A
Application number: CN202111156954.8A
Authority: CN
Inventors: 徐坤; 邝茂; 王铈汶; 易梓琦
Original assignee: Xiamen Haichen New Energy Technology Co Ltd
Current assignee: Xiamen Haichen New Energy Technology Co Ltd
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2022-01-04
Anticipated expiration: 2041-09-30
Also published as: CN113889671B

Abstract

The invention discloses an electrolyte and a lithium ion battery. The electrolyte includes: lithium salts, additives and solvents; the additive has a structure as shown in formula I,

wherein R is₁Is a bond, methylene or fluoro substituted methylene; r₂And R₃Each independently is hydrogen, fluorine or fluorine substituted C_1～6An alkyl group; r₄And R₅Each independently is hydrogen, fluorine substituted C_1～6Alkyl radical, C_1～6Alkyl or C_3～6An aryl group; and, R₁、R₂、R₃、R₄、R₅Contains at least one fluorine. The electrolyte has a fluorinated cyclic ether additive. Therefore, when the battery is charged for the first time, the stable SEI with good rigidity and toughness can be formed; the negative electrode material occurs during the charge and discharge of the battery (e.g. during the charging and discharging of the battery)Graphite), the damage of SEI is little, and the dissolution and loss of SEI components are little, so that the regeneration of SEI can be reduced, the consumption of lithium salt and solvent in the electrolyte can be reduced, and the high-low temperature cycle life of the battery can be prolonged.

Description

Electrolyte and lithium ion battery

Technical Field

The invention relates to the field of electrochemical energy storage equipment, in particular to electrolyte and a lithium ion battery.

Background

With the application of chain ether as an additive of lithium battery electrolyte, cyclic ether gradually enters the sight of researchers, and the cyclic performance of the battery can be improved by adding tetrahydrofuran and derivatives thereof as a solvent or an additive into the electrolyte according to patent and literature reports. Cyclic ethers containing two oxygen atoms, such as dioxane cyclic ethers, have also been proposed as additives or co-solvents to improve the performance of lithium ion secondary batteries. In addition, in consideration of rate performance and low-temperature performance, patent and literature reports that crown ether substances are used as additives to improve the performance of the battery, and the main principle is that the dissociation degree of electrolyte salt is improved through the action of crown ether, so that the ionic conductivity of the electrolyte is improved, and the performance of the battery is finally improved.

When the existing cyclic ether is used as an electrolyte additive, electrochemical oxidation or reduction reaction can occur under the action of voltage to generate an organic polymer interface layer, but because all the polymerized monomers are chain-shaped organic matters, the toughness of the inner layer of the interface layer is insufficient, and the outer layer of the interface layer is provided with a compact organic layer, the formed interface layer has larger impedance and poorer mechanical property, and is not beneficial to comprehensively improving the performance of a battery. Thus, the existing cyclic ether electrolyte additives still need to be improved.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, an object of the present invention is to propose an electrolyte for a lithium ion battery and a lithium ion battery.

In one aspect of the invention, an electrolyte for a lithium ion battery is provided. According to an embodiment of the invention, the electrolyte comprises: lithium salts, additives and solvents; the additive has a structure as shown in formula I,

wherein the content of the first and second substances,

R₁is a bond, methylene or fluoro substituted methylene;

R₂and R₃Each independently is hydrogen, fluorine or fluorine substituted C_1～6An alkyl group;

R₄and R₅Each independently is hydrogen, fluorine substituted C_1～6Alkyl radical, C_1～6Alkyl or C_3～6An aryl group;

and, R₁、R₂、R₃、R₄、R₅Contains at least one fluorine.

The electrolyte according to the above embodiment of the present invention has a fluorinated cyclic ether additive, and the cyclic ether can slowly chemically open a ring to generate a self-polymerization reaction, thereby improving the flexibility of the SEI inner layer; meanwhile, substitution of fluorine atoms may improve the rigidity of the SEI. Therefore, when the battery is charged for the first time, the stable SEI with good rigidity and toughness can be formed; when the volume expansion of a negative electrode material (such as graphite) occurs in the charging and discharging processes of the battery, the SEI is damaged little, and the SEI component is dissolved and lost little, so that the regeneration of the SEI can be reduced, the consumption of lithium salt and solvent in the electrolyte can be reduced, and the high-low temperature cycle life of the battery can be prolonged.

In addition, the electrolyte according to the above embodiment of the present invention may further have the following additional technical features:

in some embodiments of the invention, the fluorine is substituted for C_1～6Alkyl is selected from-CF₃、-CH₂CF₃、-CHF₂、-CF₂CF₃、-CH₂CH₂CF₃At least one of (a).

In some embodiments of the invention, said C_1～6The alkyl group is selected from at least one of methyl, ethyl, propyl and butyl.

In some embodiments of the invention, said C_3～6The aryl is at least one selected from phenyl and benzyl.

In some embodiments of the invention, the additive is selected from at least one of 2,2,4, 4-tetrafluorooxetane, perfluorooxetane, 2- (trifluoromethyl) oxirane, hexafluoropropylene oxide.

In some embodiments of the present invention, the additive is present in the electrolyte in an amount of 0.1 wt% to 5 wt%.

In some embodiments of the invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis fluorosulfonylimide, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate.

In some embodiments of the present invention, the lithium salt is present in the electrolyte in an amount of 0.5mol/L to 1.5 mol/L.

In some embodiments of the invention, the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, sulfolane, dimethyl sulfoxide, acetonitrile, malononitrile, glutaronitrile.

In some embodiments of the present invention, the electrolyte further includes other additives selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, trimethyl phosphate, and triethyl phosphate.

In some embodiments of the present invention, the content of the other additive in the electrolyte is 0 to 8 wt%.

In another aspect of the present invention, a lithium ion battery is provided. According to an embodiment of the present invention, the lithium ion battery includes the electrolyte of the above embodiment. Therefore, the lithium ion battery has excellent high and low temperature cycle performance.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a graph showing the results of a capacity retention rate test of batteries made of the electrolytes of example 1, comparative example 1, and comparative example 2.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

wherein the content of the first and second substances,

R₁is a bond, methylene or fluoro substituted methylene;

and, R₁、R₂、R₃、R₄、R₅Contains at least one fluorine.

When R is₁When the electrolyte is a bond, the electrolyte has a structure shown in a formula Ia,

The electrolyte according to an embodiment of the present invention is further described in detail below.

According to some embodiments of the invention, the fluorine is substituted C_1～6The alkyl group may be selected from-CF₃、-CH₂CF₃、-CHF₂、-CF₂CF₃、-CH₂CH₂CF₃At least one of (a).

According to some embodiments of the invention, C is_1～6The alkyl group may be at least one selected from methyl, ethyl, propyl, and butyl.

According to some embodiments of the invention, C is_3～6The aryl group may be at least one selected from phenyl and benzyl.

According to some embodiments of the present invention, the additive may be at least one selected from the group consisting of 2,2,4, 4-tetrafluorooxetane, perfluorooxetane, 2- (trifluoromethyl) oxirane, and hexafluoropropylene oxide. Therefore, the stability of the SEI with good rigidity and toughness can be further improved when the battery is charged for the first time, the regeneration of the SEI in the charging and discharging process of the battery is reduced, the consumption of lithium salt and solvent in the electrolyte is reduced, and the cycle life of the battery at high and low temperatures is prolonged.

According to some embodiments of the present invention, the additive may be present in the electrolyte in an amount of 0.1 wt% to 5 wt%, such as 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, etc. By controlling the content of the additive in the electrolyte within the above range, the performance of the additive can be further facilitated. The inventors found that if the content of the additive in the electrolyte is too low, the stability of the formed SEI may be insufficient, and the SEI may be easily damaged during the circulation process, so that the final effect may not be optimal; if the content of the additive in the electrolyte is too high, SEI that may be formed is too dense and thick, resulting in too large resistance of SEI, which is not favorable for battery cycle.

According to some embodiments of the present invention, the lithium salt may be selected from lithium hexafluorophosphate (LiPF)₆) Lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium tetrafluoroborate (LiBF)₄) At least one of lithium bis (oxalato) borate (LiBOB) and lithium difluoro (oxalato) borate (LiODFB).

According to some embodiments of the present invention, the content of the lithium salt in the electrolyte may be 0.5mol/L to 1.5mol/L, such as 0.5mol/L, 0.75mol/L, 1mol/L, 1.25mol/L, 1.5mol/L, and the like. Therefore, enough conductivity can be provided for the electrolyte, and the comprehensive performance of the battery is improved.

According to some embodiments of the present invention, the solvent may be selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), Propylene Carbonate (PC), sulfolane, dimethyl sulfoxide, acetonitrile, malononitrile, and glutaronitrile.

According to some embodiments of the present invention, the electrolyte of the present invention may further include other additives, and the other additives may be selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, trimethyl phosphate, and triethyl phosphate. This can further improve the high-low temperature cycle performance of the battery.

According to some embodiments of the present invention, the content of the other additive in the electrolyte may be 0 to 8 wt%, for example, 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, etc. This can further improve the high-low temperature cycle performance of the battery.

In addition, it should be noted that the lithium ion battery also has all the features and advantages described above for the electrolyte, and thus detailed description is omitted here.

The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.

Example 1

In an argon atmosphere glove box with the moisture content of less than or equal to 1ppm, 30g of EC and 70g of EMC are mixed, then dried lithium salt is added into the mixed solvent to obtain 13.9g of lithium hexafluorophosphate solid in total, after lithium hexafluorophosphate is completely dissolved, 1.15g of fluorinated cyclic ether 2,2,4, 4-tetrafluorooxetane is added, 1.15g of vinylene carbonate is added in total, and the electrolyte is obtained after uniform mixing. In the electrolyte, the solvent composition was EC: EMC 3:7 (mass ratio), the lithium salt concentration was 1mol/L, the content of the fluorinated cyclic ether additive was 1% of the total mass of the electrolyte, and the content of the vinylene carbonate additive was 1% of the total mass of the electrolyte.

Example 2

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the fluorocyclic ether additive was replaced with perfluorooxetane, and the perfluorooxetane content was adjusted to be 1% by mass of the total electrolyte.

Example 3

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the fluorocyclic ether additive was replaced with 2- (trifluoromethyl) ethylene oxide, and the content of 2- (trifluoromethyl) ethylene oxide was adjusted to be 1% by mass of the total mass of the electrolyte.

Example 4

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the fluorocyclic ether additive was replaced with hexafluoropropylene oxide, and the content of hexafluoropropylene oxide was adjusted to be 1% of the total mass of the electrolyte.

Example 5

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the content of 2,2,4, 4-tetrafluorooxetane was adjusted to be 1% by mass of the total electrolyte.

Example 6

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the fluorocyclic ether additive was replaced with perfluorooxetane, and the perfluorooxetane content was adjusted to 0.1% by mass of the total electrolyte.

Example 7

An electrolyte was prepared in substantially the same manner as in example 1, except that vinylene carbonate was not added, and the fluorocyclic ether additive was replaced with perfluorooxetane, and the perfluorooxetane content was adjusted to be 5% by mass of the total electrolyte.

Comparative example 1

An electrolyte was prepared in substantially the same manner as in example 1, except that the vinylene carbonate additive and the fluorinated cyclic ether additive were not added.

Comparative example 2

An electrolyte was prepared in substantially the same manner as in example 1, except that the fluorinated cyclic ether additive was not added and the vinylene carbonate content was adjusted to 1% by mass based on the total mass of the electrolyte.

Test example

The electrolytes of examples 1 to 7 and comparative examples 1 to 2 were used to prepare test batteries, the positive electrode material used in the batteries was NCM622 material, the negative electrode material used in the batteries was modified natural graphite material, the designed capacity of the batteries was 1A · h, and the electrolyte injection amount of the batteries was 4.0 g. And carrying out charge-discharge cycle test on each battery on a charge-discharge instrument, wherein the test temperature is 25 ℃, the cycle rate is 1C, and the charging voltage is 3.0V-4.2V. And calculating the capacity retention rate after circulation, wherein the calculation formula is as follows: the capacity retention rate after the n-th cycle was ═ 100% (discharge capacity after the n-th cycle/first-cycle discharge capacity), and the results are shown in table 1. The curves of the capacity retention rate test results of the batteries made of the electrolytes of example 1, comparative example 1 and comparative example 2 are shown in FIG. 1.

TABLE 1 Capacity Retention test results

	Retention ratio of 500 cycles of capacity (%)
		Example 1	97.4
Example 2	93.5
		Example 3	94.2
Example 4	88.7
		Example 5	96.3
Example 6	91.3
		Example 7	84.1
Comparative example 1	71.2
		Comparative example 2	85.8

Test results show that the cyclic performance of the battery can be remarkably improved by adding the fluorinated cyclic ether additive into the electrolyte. Under the same addition amount, the fluorinated cyclic ether additive has better effect of improving the performance of the battery than the conventional vinylene carbonate additive. From the results of example 6 and comparative example 2, it can be seen that the fluorinated cyclic ether additive, although having a reduced performance at lower addition levels, is superior to the higher levels of conventional vinylene carbonate. From the results of example 7 and comparative example 2, it is known that the cyclic ether fluoride additive affects the cycle performance of the battery at a higher addition amount, which may be due to the increase in interfacial resistance caused by the high cyclic ether fluoride additive, but the cycle performance of the battery is close to that of the battery using the conventional vinylene carbonate additive. In addition, from the results of examples 1 and 5, and comparative examples 1 and 2, it was found that the use of the fluorocyclic ether additive in combination with vinylene carbonate can further improve the cycle performance of the battery.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. An electrolyte for a lithium ion battery, comprising: lithium salts, additives and solvents; the additive has a structure as shown in formula I,

wherein the content of the first and second substances,

R₁is a bond, methylene or fluoro substituted methylene;

and, R₁、R₂、R₃、R₄、R₅Contains at least one fluorine.

2. The electrolyte of claim 1, wherein the fluorine is substituted for C_1～6Alkyl is selected from-CF₃、-CH₂CF₃、-CHF₂、-CF₂CF₃、-CH₂CH₂CF₃At least one of (a).

3. The electrolyte of claim 1, wherein C is_1～6The alkyl group is selected from at least one of methyl, ethyl, propyl and butyl.

4. The electrolyte of claim 1, wherein C is_3～6The aryl is at least one selected from phenyl and benzyl.

5. The electrolyte of claim 1, wherein the additive is selected from at least one of 2,2,4, 4-tetrafluorooxetane, perfluorooxetane, 2- (trifluoromethyl) oxirane, and hexafluoropropylene oxide.

6. The electrolyte of claim 1, wherein the additive is present in the electrolyte in an amount of 0.1 wt% to 5 wt%.

7. The electrolyte of claim 1, wherein the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (fluorosulfonyl) imide, lithium tetrafluoroborate, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate;

optionally, the content of the lithium salt in the electrolyte is 0.5 mol/L-1.5 mol/L.

8. The electrolyte of claim 1, wherein the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, sulfolane, dimethyl sulfoxide, acetonitrile, malononitrile, and glutaronitrile.

9. The electrolyte of claim 1, further comprising other additives selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, trimethyl phosphate, and triethyl phosphate;

optionally, the content of the other additives in the electrolyte is 0-8 wt%.

10. A lithium ion battery comprising the electrolyte according to any one of claims 1 to 9.